The present invention relates to a method for determining a particle concentration and, more particularly, for determining a particle concentration of a continuous medium in a container.
A method of determining the particle concentration of dissolved substances using the scattering of laser light is disclosed in European Patent Application No. 7 44 28 A1, which is incorporated herein by reference. Blood components can be determined using such method. The quantitative determination of the particle concentration requires measuring the intensity of the primary beam and the intensity of the scattered radiation of the sample occurring at specific angles. The measured signals being corrected in order to compensate for altered physical conditions in the sample among the different measurements or within one measurement. The corrected measured signals are then assigned to the concentration of the system component to be determined. In accordance with the known teaching, the measurements are made within a scattering angle range in which there is a maximum dependence of the scattered-radiation intensity on the concentration of the respective component to be determined.
The sensor surfaces are typically comprised of a plurality of layers including a light-insensitive cover layer in which defined linear apertures are arranged to permit light to pass through to the light-sensitive layers situated underneath the cover layer. These defined linear apertures must be precisely assigned to the object to be measured as well as to the light source.
If there is a need to measure a medical suspension, such as blood, that is being passed through a tube, the tube must be precisely positioned with respect to the corresponding sensor surface having the linear apertures. This necessitates a precision-type design that is costly and prone to interference, to the extent that the tube is not securely fixed with respect to the sensor surface.
The object of the present invention is to provide an improved method of determining a particle concentration of a continuous medium that is adapted to be carried out using relatively simple measurement set-up and that is not readily susceptible to disturbances. It is a further object of the invention to accurately measure the particle concentration of a medical suspension, such as blood, that is contained on or passed through a tubular measurement receptacle (tube).
In accordance with the illustrative embodiments, demonstrating features and advantages of the present invention, there is provided a method for determining the particle concentration of a continuous medium in a container that includes the following steps: aligning a light beam from a light source through a particle-loaded, continuous medium, to the light-sensitive surface of a position-sensitive sensor, the light beam being so directed at the light-sensitive surface that the light scattered by the particles assuming, on average, a different position than the unscattered light; determining the deviation of the midpoint of the scattered light on the light-sensitive surface from the midpoint of the unscattered light on the light-sensitive surface; and correlating the deviation to the particle concentration.
The position-sensitive sensor is used on the basis of a large-surface area, light-sensitive surface. Such surface is preferably in the form of a PIN photodiode. Information can be provided about positioning through the use of at least two position dependent taps (contacts) even thought the light-sensitive surface has a homogeneous form. Using a sensor of this kind, the scattering behavior of the particle-loaded, continuous medium can be measured readily without a costly measurement set-up and with reduced susceptibility to failure. The measuring set-up is selected in such a way that the light beam altered by scattered light, on the average, assumes a different position than the light beam that is not scattered. This positional change, which is sensed by the light-sensitive surface of the position-sensitive sensor, can be drawn upon as a measure for the number of particles. That means that a corresponding positional change can be correlated to a specific particle concentration.
An important aspect of the method is that the light beam be directed at the light-sensitive surface in such a way that the light scattered by the particles assumes, on the average, a different position than the unscattered light. This can be achieved in accordance with a first variant of the embodiment in that the light beam is directed at right angles at the light-sensitive surface of the position-sensitive sensor, and in that the light-sensitive surface is partially covered so that the light beam striking upon this surface is at least partially covered or blocked.
Alternatively, the light beam can be directed at an angle (w) at the light-sensitive surface of the position-sensitive sensor.
In accordance with one preferred embodiment of the method according to the present invention, more than one light beam can be directed at the light-sensitive surface. These different light sources can also have different wavelengths. This makes it possible to determine the influence of the light scatterer on various wavelengths. If the light sources are simultaneously turned on, a differential signal can be detected, which can be used to determine, for example, whether the particles in question are scattering light substantially identically or variably.
A device for implementing the afore-mentioned method according to the present invention includes at least one light source, one receptacle for receiving or for directing the particle-loaded continuous medium, and a position-sensitive sensor having two current outputs configured at a distance from one another.
Using the device according to the present invention, it is possible to use one single, simply designed light sensor that makes use of only two electrical signals. In this manner, one can eliminate parameter scattering of components, as well as their temperature sensitivity and ageing effects.
In accordance with one preferred specific embodiment of the present invention, a simple light-emitting diode or a laser diode can be used as a light source without employing any additional optical systems.
Measurement receptacles of different types can be advantageously employed. They can be flat or in the form of a tube. Further, the receptacles can be rigid or flexible. For example, translucent tubes used to hold medical suspensions (e.g., blood) can be readily utilized.
The measuring method and the corresponding device exhibit a high sensitivity so that very small particle concentrations are able to be determined. Furthermore, there is no need to perform expensive adjustments on the light source and sensor since measuring signals can be received even when working with slightly shifted images.
Other objects, features and advantages of the invention will be readily apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the drawings.